122 FERTILISERS (GENERAL METHODS)
The percentage (x) of NaN03 or KNO3 may be calculated by the formula,
a X ioo
x = _ .
2. JODLBAUR'S MODIFIED KJELDAHL METHOD. This is applied in the
manner indicated under J) for the total nitrogen. With nitrates 0-5 gram
is taken, and with mixed fertilisers i gram. N x 0-1647 — NuN08;
N X 0-1387 == KN03.
The result obtained by this method must, of course, be diminished by
the porportions of animoniacal and organic nitrogen (found under A and
C. Organic Nitrogen.—This is determined by (Jlxcli's modification
of the Kjchlahl method :
Into a long-necked, pear-shaped flask of good resistant; glass holding
about 250 c.c.1 from r to 5 grains
(according 1o the nitrogen content)
of the substance are introduced,2
together with :»o 25 e.c. of />/W-
phosnlpliiiric acid (123 grams of
phosphoric anhydride dissolved in
i litre of sulphuric acid of 66°
Baume), 2 3 drops of 1.0% platinum
chloride solution, aiul 0-2 (»•;•} gram
of copper oxide.
The llask is closed with a, small
funnel or, better, with a, light glass
bull) drawn out to a point, at one
end, and is then placed sloping on
an asbestos-covered gau/.e and
heated, at. first with a. small flame;
and then to boiling until a clear and
alums!, if not quite, colourless solu-
tion is obtained. In this way the
organic, nitrogen is wholly converted
into ammonium sulphate.
When cold, the liquid is carefully
diluted with water and washed out
into a, flask of about i litre capacity.
The liquid is then rendered alkaline
with excess of sodium hydroxide
solution (about jo%) and the am-
monia distilled, an apparatus similar to (hat shown in l-'ig. j being used.
The flask J contains the alkaline liquid to be distilled, the bulb//serves to
retain any alkali spurting over and is formed of two concentric glass bulbs, the.
1 Suitable Husks ami other itmsssunes for the Kjeldahl method arc wild.
a With liquids, tnich volume or weight is taken UK earrespunds with i 5 KI";IIIIH °f
solid, substance, according to the nitrogen content. The liquid is then evaporated to
dryness in the Kjeldahl flask itself,
rounding air (about i hour is sufficient), the two tubes are